Typically, in present-day lube oil formulations for internal combustion engines, phosphorus-containing compounds, such as zinc dialkyldithiophosphate (ZDDP), are added to the lube oil formulation to provide improved anti-wear properties. However, it has been found that phosphorus from phosphorus-containing compounds becomes deposited on the catalysts in catalytic converters, thereby decreasing the efficiency of catalytic converters over time. At the present time automotive lube oils typically contain a maximum of about 0.10 to about 0.14 wt. % phosphorus. To reduce the rate at which catalytic converters become fouled by phosphorus, it has been suggested that the maximum phosphorus content of lube oils be reduced to a range of about 0.05 to about 0.08 wt. %.
The use of carbonates in lubes oils is known. U.S. Pat. Nos. 2,340,331 and 2,387,999 disclose the use of diethyl, diamyl, dilauryl, diphenyl, dicresyl, di-o-cresyl, dibenzyl, mono-ethyl, and monophenyl carbonates in lube oils to increase the extreme pressure characteristics and reduce the rate of wear of lubricating oils.
European Patent Publication No. 89,709 discloses the use of organic carbonic esters of higher alcohols in lubricants for internal combustion engines. Wear and Coefficient of Friction test data are reported.
U.S. Patents 4,707,284 and 4,801,391 disclose lube oils having improved anti-wear properties wherein the lube oil comprises a basestock, diphenyl carbonate and a metal dialkyldithiophosphate salt. It is there disclosed that cyclic carbonates, such as ethylene carbonate, have relatively low solubility in lube oils, and are not preferred, and notes that the solubility of ethylene carbonate in basestock is about 0.04 wt. % at 25.degree. C., while the solubility in a fully-formulated motor oil is about 0.2 wt. % at 25.degree. C. The diphenyl carbonate of the patent is illustrated in fully-formulated lubricating oils containing viscosity index improver, antioxidant, dispersant, detergent and anti-foamant additives, with and without the addition of zinc dialkyldithiophosphate anti-wear additives.
While diphenyl carbonate possesses adequate solubility in fully-formulated lubricating oils, the formulation of lubricating oils conventionally involves the dissolution in a lubricating oil basestock of an additive package comprising a concentrate of the active ingredients, other than viscosity index improver, to prepare the fully-formulated oil.
U.S. Patents 4,707,284 and 4,801,391 disclose lubricating oils having improved anti-wear properties comprising basestock, a diphenyl carbonate and a metal dialkyldithiophosphate salt. The concentration of the diphenyl carbonate is given at from 0.1 to 1.5, relative to the basestock.